Asymmetrical Absorption and Surface-Enhanced Raman Scattering Enhancement by Silver Nanoflower Metasurface

A metasurface composed of silver nanoflower arrays, which exhibit asymmetrical absorption and surface-enhanced Raman scattering (SERS) due to hybrid plasmonic effects, is reported. The silver nanoflowers are fabricated by oblique deposition of silver on a polymer nanohole array on a glass substrate, forming petal-like semicontinuous thin films on the inner walls of the holes. Depending on the deposition angle, three- or five-petal nanoflowers are obtained. The nanoflower arrays show strong reflection from the air side and broadband and wide-angle absorption from the glass side, as a result of transmission surface plasmon resonance and localized surface plasmon resonance, respectively. The three-petal structure, which absorbs most of the incident light from the glass side, induces a localized enhancement of electric field in the center of each nanohole, providing a high-sensitivity SERS substrate. The SERS performance of the metasurface by direct measurement and near-field simulation is demonstrated.